Microwave multiband tuner



Get.. 8, 1946. A. H. TURNER v2,408,896

' I MICROWAVE MULTI'BAND TUNER' v Filed Nov. 29, 1945 2`Sheets-Sheet 1 l 'Bg I Cttomeg 011 3 1946- A. H. TURNER MICROWAVE MULTIBAND TUNER 4 2 sheets-sheet 2 Filed Nov. 29, 1945 t m n e D n 3 ./Zgralfjf. maar'. N CM Ctt'orneg Patented Oct. 8, 1946 MICROWAVE MULTIBAND TUNER Alfred H. Turner, Collingswood, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application November 29, 1943, Serial No. 512,107

6 Claims.

l This invention relates generally to ultra-highfrequency apparatus and particularly to an improved microwave multiband tuner for covering a plurality of relatively wide microwave bands.

One of the conventional methods of tuning at ultra-high frequencies is to employ a resonant line of suitable design across one end of which is connected a variable capacitor having a relatively high maximum capacity. Such an arrangement provides a theoretical limit of 1 to 2v between minimum and maximum frequency adjustments. In practice, the theoretical limit is not attainable because of non-uniform circuit constants. In addition, the loading effect of the device to which the tuner is connected reduces the practicable tuning frequency band.

`The instant invention is an improvement upon applicants copending application Serial No. 481,215, filed March 3l, 1.943, entitled Ultra high frequency tuner, which is assigned to the same assignee as the instant application. Both inventions contemplate the use of a resonant line connected at one end to a suitable utilization circuit. The opposite ends of the line are connected together through one or more variable capacitors and an inductive element having an inductance of the order of that of one of the lines. The resulting circuit comprises a parallel resonant circuit including the utilization device and the resonant lines, having a series-tuned circuit including the capacitive and the inductive elements connected across the ends of the lines remote from the utilization device. Adjustment of the reactance of the series capacitors effectively provides simultaneous adjustment of both the capacitive and inductive reactances of the circuit. Such an arrangement provides a theoretical limit of one to three between the minimum and maximum tuning frequency limits. Of course, the theoretical limit may not be attainable in actual practice, but the practical limits substantially exceed those possible with the conventional tuning arrangement described heretofore.

The tuning means comprises a pair of resonant lines of the order of one quarter to one half wavelength at the operating frequency which terminate at one end in the utilization device and at the other end in iixed capacitor electrodes. Two movable capacitor electrodes are disposed invariable capacitive relation to separate ones of.

the xed capacitive elements and arranged to vary simultaneously the capacity between each fixed and movable-electrode. A lumped inductive element, such as, for example, a relatively small helix, is connected directly between the movable capacitive elements, and may be arranged to rotate with them. The eifective inductanceof the inductive element is of the order of that employed for one of the resonant lines. It should be understood that two or more tuning .units of the type described may be connected to diiferent utilization circuits, such as, for example, the input and output circuits of the same ordiiferentthermionic tubes. It should also be understood that the rotating capacitive elements may be suitably ganged by means of any convenient mechanical arrangement.

The improvements which the instant invention comprises with respect tovapplicants copending application described heretofore, include means for tuning over a plurality of relatively wide ultra-high-frequency bands, and especially means for maintaining substantially constant the pass band of the tuning apparatus over all portions of each of the tuning ranges. Furthermore, the inductive coupling between the various tuned circuits is supplemented by capacitive coupling in the regions of voltage nodes in the tuned circuits, for providing additional coupling between said circuits over predetermined portions of the tuning bands. Simple switching means is provided for switching between the various tuning wave bands.

It should be understood-that the instant invention may employ either open resonant lines or coaxial resonant lines, as described in applicants copending application identified heretofore, as portions of the resonant circuits.

Among the objects of the invention are to providean improved method of and means for tuning an ultra high frequency circuit. Another object is to provide an improved method of and means for varying simultaneously the inductive and capacitive reactance of an ultra high frequency circuit. A further object of the invention is .to provide an improved method of and means for tuning an ultra high frequency circuit over a relatively wide band of frequencies. Another object is to provide an improved method of andmeans for varying simultaneously the series inductive and capacitive reactance in a plurality of ultra high frequency tuned circuits. A still further object of the invention is to provide an improved method of and means for tuning a concentric ultra high frequency kline by adjusting simultaneously the series inductive and capacitivereactances connected to said line.

Additional objects of the invention include an improved method of and means for tuning microwave .apparatus over a plurality of microwave frequency bands. Another object of the invention is to provide an improved microwave multiband tuner having substantially uniform bandpass characteristics and providing substantially uniform coupling between coupled tuned circuits throughout the frequency range of said tuner.

'I'he invention Will be described in greater detail by reference to the accompanying drawings of which Figure 1 is a schematic circuit diagram of a pair of coupled circuits connected according to the invention; Figure 2 is a family of graphs indicating the voltage distribution on a tuned line comprising one component of the circuit of Figure l; Figure 3 is a schematic circuit diagram of the radio frequency, mixer and local oscillator circuits of a multiband microwave receiver including features of the invention, and Figure 4 is a perspective fragmentary view of the structural details of a preferred embodiment o1 the invention as shown schematically in Figure 3.

Similar reference characters are applied to similar elements throughout the drawing.

Referring to Figure l, a utilization circuit, comprising the anode circuits of thermionic tubes 24 and 25, and having an inherent capacitance represented by the interelectrode tube capacities and the inter tube capacities, is connected to one end of a first resonant line, represented by an inductance 4, and to one end of a second resonant line, represented by a second inductance 5. The remaining terminals of the resonant lines 4 and 5 terminate, respectively, in fixed capacitive elements E and l. A first movable capacitive element 8 is disposed in variable capacitive 'relation with the first xed capacitive element 6. The juxtaposed capacitive elements 6, 8 form a capacitor, which may be varied. A second movable capacitive element 9 is disposed in similar variable capacitive relation to the second fixed capacitive element l. A third inductive element l0, which, for example, may be a small substantially rigid helix, having an inductance of the order of the inductance of one of the resonant lines, is connected between the first and second movable capacitive elements 8 and 9. The third inductive element I0 may, if desired, be rotated simultaneously with the movable capacitive elements 8 and 9, These movable capacitive elements may be individually or interdependently rotated.

Similarly, the control electrodes, for example, of a double triode tube 34 are each connected respectively to one end of third and fourth resonant lines, represented by the inductances 4' and 5', respectively, ends'of the third and fourth resonant lines, represented by the inductances 4', 5', respectively, are connected to fixed capacitive elements 6', 1', respectively. Similarly, movable capacitive elements 8', 9 are connected together through a second small substantially rigid helix I0 having an inductanoe of the order of the inductance of one of the resonant lines.

The resonant lines 4, 4', 5, 5', preferably are symmetrically arranged and equidistant from each other to form the diagonally opposite corners of a square or a rectangle whereby the mutual inductive coupling between the various resonant lines is maintained at a substantially constant value. Y

The mutual inductive coupling between the several resonant lines is supplemented by the distributed capacities between the tuning capacitors 6', 8' and 1, 9, respectively, and between the tuning capacitors 6, 8 and l', 9', respectively, as indi- Likewise, the remaining tively coupled to the input loop 22.

cated by the phantom capacitors cl, c2, It Will be seen that the distributed capacities cI and c2 will supplement the coupling between the resonant lines at the high frequency end of the tuning band as illustrated in graph (a) of Figure 2.

A small fixed capacitor I I is connected between the anode end of the resonant line 4 and the control electrode end of the resonant line 5'. A similar fixed capacitor I2 is connected between the control electrode end of the resonant line 4' and the anode end of the resonant line 5. These capacitors are connected to the resonant lines at points which correspond to voltage nodes at the high frequency end of the tuning band and hence correspond to regions of voltage maxima at the low frequency end of the tuning band, thereby providing appreciable coupling at the low frequency end of the tuning band.

When additional inductive elements, not shown, are connected in series with the tube ends of the resonant lines at the points marked (x) to provide tuning throughout an additional relatively lower frequency band, the capacitors II, I2 effectively are moved nearer the tube ends of the resonant circuits, thereby improving the mutual coupling between the lines at the low frequency ond of the lowest frequency tuning band. 'I'he tuning range of the tuned coupled circuits further may be adjusted or extended by means of fixed variable capacitors 53, 54 connected, respectively, between the anodes of the tetrode tubes 24 and 25 of the control electrodes of the double triode tube 34 to increase the effective loading capacitances of the utilization devices.

Referring to Figure 3, an ultra-high frequency multiband receiver circuit comprising an ultra high frequency amplifier, an ultra high frequency oscillator and an ultra high frequency mixer or iirst detector. is shown in combination with tuning circuits of the general type illustrated in Fig,

ure l and described in detail heretofore. A concentric transmission line 2| connected, for example, to a suitable receiving antenna, not shown, is connected to one end of an input coupling loop 22. The remaining end of the input coupling loop 22 is connected to ground through a variable tuning capacitor 23. Y An ultra high frequency balanced amplifier such as, for example, a pair of tetrode tubes 24, 25 is self-biased by means of a conventional common cathode resistor 2B and cathode bypass capacitor 21 which are connected between the cathodes and ground. The control electrodes of each of the tubes are connected to the ends of a center-tapped grid inductor 28 which is induc- The center terminal of the grid inductor is grounded.

The anodes of the first and second triodes 24, 25 are connected each to one terminal of corresponding first and second helical low band inductors I5, I6. The remaining terminals of the low band inductors I5, I6 are serially connected, respectively, to first and second helical high band inductors I1, I8. The remaining terminals of the high band inductors I'I, I8 are connected to the ends of short resonant lines 4, 5. The remaining terminals of the resonant lines 4, 5 are terminated. respectively, in first and second fixed capacitive elements B and 1 The movable capacitive elements 8 and 9, which are in capacitive relation., respectively,y with the fixed capacitive elements 6, and l, are connected together through a compact bunched helical inductive element I0 of the type described heretofore. Operating potentials for the anodes of the ytwo triodes 24, 25 are provided from any suitable source, not shown, and applied to the respective electrodes through suitable isolating resistors 3l, 32 and 33.

A mixer or converter stage includes a 'double triode 34 having the two anodes thereof connected together and connected to the primary of an intermediate frequency transformer 36. The cathode is connected to ground. The control electrodes of the two triodes of the double triode 34 are each connected to one end of separate resonant circuits comprising second low band inductors I5 and I6 respectively connected in series with second high band inductors I1 and I8' and resonant lines 4' and 5. The resonant lines 4' and 5' are inductively coupled to the resonant lines 4 and 5 of the radio frequency amplier anode circuit. The resonant lines 4', 5' are tuned by a second tuning unit 6', 1', 8', 9', I', of the type described heretofore, which is serially connected to the lines 4', 5', and with the corresponding low band and high band inductors I', I5', Il', I8'. A grounded center-tapped resistor network 31, 38 is connected between the common terminals of the inductive elements I5', I1' and I6', I3', to provide a d-c grid return circuit for the balanced converter.

An ultra high frequency oscillator includes a double triode 44 having its cathode connected to ground through a cathode resistor 45 and cathode capacitor 46. The grid circuit of the oscillator is comprised of a single turn loop 41 terminating in the two control electrodes and having its center-point grounded through a grid resistor 48.

The anode circuit of the push-pull oscillator includes a third tuning unit 6", 1", 8", 9", I0" serially connected with corresponding lines 4", 5 and low band and high band inductors I5", I6", I1", I8". Anode potential is applied to the two anodes through anode resistors 49, 50.

The three tuning units described heretofore may be ganged as indicated by the dash lines 5I. The balanced oscillator circuit is coupled to the converter input circuit by means of mutual inductive coupling between the tuned resonant lines in any manner known in the art, It should be understood that the constants of the circuits will be so selected that the desired intermediate frequency may be derived from the converter anode circuit.

For example, the several tuning capacitors may be of a conventional type providing a capacity range of the order of from one to ten micromicro-farads. Circuits of the type described have been constructed to provide suitable tuning over ranges extending from to 130 megacycles and to 230 megacycles. These ranges could be extended readily by proper selection of circuit constants, and by adapting the constructional features to the desired frequency ranges in a manner well known in the art.

|The three resonant circuits may be matched, or the low frequency limits thereof extended, by means of variable capacitors 53, 54 and 55 connected respectively in shunt with the corresponding tube ends of the resonant circuits. Similarly, band switching of the three resonant circuits is obtained by means of three four-pole, two position wafer type switches 56, 51 and '58 which selectively short-circuit the several low band inductors I5, I6, I5', I5', I5" and I6" The three switches 56, 51 and 58 may be ganged together and ganged to a band switch 59 adapted to iorten the grid loop 41 of the oscillator circuit.

6 The gauging of the four swtchesis indicated in the drawings by the dash line 60.

The supplementary coupling `capacitors are connected in the same manner as described heretofore in the circuit of Figure 1. The capacities ci, c2 are indicated by dash lines between the B., F. amplifier and converter tuned circuits. Similar capacities c3, c4, also shown in dash lines, indicate coupling between the converter and oscillator tuners. The two coupling capacitors Il, i2 are connected between the tube ends of the resonant circuits of the R. F. amplifier and converter in the same manner as indicated in the circuit of Figure l, Similar capacitors II and i3 couple between the tube ends of the resonant circuits of the converter and oscillator tubes.

Referring to Figure 4, a preferred mechanical construction employing the several features of the invention comprises a plurality of variable capacitive elements indicated by reference numerals conforming to the equivalent elements of the circuit of Figure 3. The inductive elements I5, I 0', I are shown as small helical inductors secured between the rotatable capacitor plates 8, I9, 8', 9', 8", 9", respectively. The low band inductors are shown as small substantially rigid helices I5, I6, i5', I5', I5" and I6. rIhe high band inductors are shown as similar small substantially rigid helices I1, I8, I1', I8', I1", i8" which are supported between the lower contacts of the corresponding wave band switches and one end of the corresponding resonant lines 4, 5, 4', 5', 4", 5, respectively. It should be noted that the low band helices are secured directly to the corresponding band switch terminals to minimize residual circuit reactances and provide convenient support. The band switches 58, 51, 58 may be the conventional wafer type band switch employed in commercial multiband tuners wherein the various switch wafer elements are insulated from each other. The various fixed capacitor plates B, 1, 5', 1', 5", 1" may be secured to insulating base supports 53, E5 for convenient mounting to the receiver chassis, not shown. Similarly, the band switches 56, 51, 58 may be supported in any convenient manner by the receiver chassis and provided with a suitable actuating mechanism, not shown. The supplementary tuning capacitors 53, 54, 55 and the supplementary coupling capacitors II, I2, II', I2 are indicated schematically to simplify the drawings. lln practice, these capacitors should be the small tubular type well known in the art.

Shielding, of the type indicated by the fragmentary shield portion 55, may be employed in accordance with recognized shielding procedure between any of the tuned circuits requiring isolation. It should be understood that inductive coupling between the various resonant circuits may be adjusted by adjusting the position and size of the shields isolating said circuits.

Thus the invention described comprises improvements of the invention described in applicants copending application identified heretofore, wherein multiband tuning is provided at microwave frequencies, and novel capacitive coupling is included to supplement the inherent inductive coupling between a plurality of circuit tuning elements, thereby to provide substantially uniform band width throughout the tuning range and substantially constant reaction between said coupled circuits.

I claim as my invention:

1. Ultra-high-frequency apparatus including a plurality of inductively coupled tuning circuits lmoeras@ `coupling between said circuits throughout the tuning range of said circuits.

2. Multiband microwave apparatus including a plurality of inductively coupled microwave tuning circuits each comprising a pair of resonant lines and adjustable means for tuning said lines, a plurality of coupling capacitors, a plurality of loading inductors, means for selectively and simultaneously interposing one of said loading inductors in each of said resonant lines to change the tuning waveband thereof, and means connecting said capacitors between the resonant lines of different ones of said coupled circuits at predetermined points on said lines to provide predetermined microwave coupling between said circuits throughout the tuning range of said circuits.

3. Ultra-high-frequency apparatus including a plurality of inductively coupled tuning circuits each comprising a pair of resonant lines and adjustable means for tuning said lines, a plurality of coupling capacitors, and means connecting said capacitors between the resonant lines of diiierent ones of said coupled circuits at points on said lines corresponding to the regions of voltage antinodes at the limits of said circuit tuning ranges to provide predetermined coupling between said circuits throughout said tuning range of said circuits.

4. Multiband microwave apparatus including a plurality of inductively coupled microwave tuning circuits each comprising a pair of resonant lines and adjustable means for tuning said lines, a plurality of coupling capacitors, a plurality of loading inductors, means including separate short-circuiting means shunting each of said inductors for selectively and simultaneously interposing one of said loading inductors in each of said resonant lines to change the tuning waveband thereof, and means connecting said capacitors between the resonant lines of diierent ones of said coupled circuits at predetermined points von said lines to vprovide predetermined'microwave coupling between said circuits throughout the tuning range of said circuits.

5. Multiband ultra-high-frequency apparatus including a. plurality of inductively coupled tuning circuits each including, in combination, a pair of resonant lines, a pair of adjustable capacitive elements each having at least a fixed electrode vand a movable electrode, an inductive element having an inductance at least of the order of the inductance of one of said resonant lines.

' means connecting said inductive element between said movable electrodes of said capacitive elements, means connecting one extremity of each of said resonant lines to a different one o1' said iixed electrodes of said capacitive elements, a. utilization device, means connecting the remaining ends of said lines to said utilization device, and means for adjusting simultaneously the capacity of all of said capacitive elements to vary simultaneously the effective series inductive and capacitive reactance of all of said circuits; a plurality of loading inductors, means for selectively and simultaneously interposing one of said loading inductors in each of said resonant lines to change the tuning waveband thereof, a plurality of coupling capacitors, and means connecting said capacitors between the resonant lines of diierent ones of said coupled circuits at predetermined points on said lines to provide predetermined coupling between said circuits throughout said tuning bands.

6. Multiband microwave apparatus including a plurality of inductively coupled microwave tuning circuits each including a pair of inductive elements `and adjustable means for tuning said circuits, a plurality of coupling capacitors, a. plurality of loading inductors, means for selectively interposing said loading inductors in each of said tuning circuits to change the tuning waveband thereof, and means connecting said capacitors between said inductive elements of different ones of said coupled circuits to provide predetermined microwave coupling between said circuits throughout the multiband tuning range of said circuits.

l ALFRED H. TURNER. 

